1. Field of the Invention
The field of the invention is that of (dense) wavelength division multiplexing ((D)WDM) networks, and more particularly that of the transmission of data (or optical signals) in such networks.
2. Description of the Related Art
As the person skilled in the art knows, wavelength division multiplexing is a technique that optimizes the use of data transmission resources (for example optical fibers) of an optical network. Such optimization is particularly important if those resources are limited or become insufficient because of the connection of new communications stations (or nodes), or in order to limit the cost of the network.
Wavelength division multiplexing is insufficient in some situations in which the network architecture needs to be optimized.
Many solutions to this have been proposed, for example integrating passive multiplex add/drop devices such as optical couplers or optical add and drop multiplexers (OADM), possibly of the reconfigurable type (R-OADM), or the co-propagation of upstream and downstream traffic in the same fiber by sharing its bandwidth. Those solutions may still be insufficient, however.
The extent of an optical network is limited by its range, i.e. by the power necessary to transmit multiplexes between the network access node (also known as the “hub”, which is generally connected to a federator network (also known as the “backbone”), and the communications station farthest therefrom. To economize on this power, there has been proposed an unbalanced mode of coupling traffic coming from a given communications station and traffic coming from optical fiber portions on the upstream side of that communications station. For example, a communications station near the hub is the subject of 10%/90% coupling and a communications station near the edge of the network is the subject of 50%/50% coupling. Optimizing the coupling ratios in this way loosens the constraint related to power, but cannot eliminate it entirely.